1. Field of the Invention
The present invention relates to a method and an apparatus for estimating the remaining service life of a material and more particularly, to a remaining service life prediction method and apparatus well suited for application to a metal material which is used in high-temperature water and under neutron irradiation and which undergoes stress corrosion cracking.
2. Description of the Related Art
Since a material such as austenitic stainless steel used in a nuclear reactor is subjected to irradiation with radioactive rays in a corrosive environment of high-temperature water, it may possibly undergo irradiation-assisted stress corrosion cracking (IASCC) ascribable to corrosion damage or deterioration in the material. The IASCC is classified into the transgranular type and the intergranular type, depending upon the form of a fracture surface developed.
If an accident should take place in such a nuclear reactor plant, it will have very serious consequences. It is accordingly imperative that any accident is prevented from occurring. As a process for suppressing the IASCC, hydrogen injection has been presently proposed. With this process, the material is doped with hydrogen, thereby reducing a dissolved oxygen concentration or lowering corrosion potential.
In addition, the safety of the material from the stress corrosion cracking has heretofore been ensured by making an annual routine inspection to verify the use thereof since the last routine inspection. With this method, the safety at the time of the inspection can be checked, but the service life of the material cannot be predicted as to whether the stress corrosion cracking will arise before the next routine inspection.
Additionally, a service life diagnostic system for a metal material concerning the stress corrosion cracking is disclosed in the official gazette of Japanese Patent Application Laid-open No. 69942/1989. This technique consists in that the stress corrosion cracking characteristic of the material is evaluated by obtaining the quantity of charges versus the active dissolution of a fresh metal surface and the localization factor of corrosion.
With the aforementioned technique, in estimating the remaining service life of a sample, the quantity of charges versus the active dissolution of the fresh metal surface and the localization factor of the corrosion must be obtained. This method has the problem that the remaining service life of the material which becomes brittle due to the irradiation with particles cannot be estimated merely by subjecting the sample to a simple test.